This invention relates to a novel composite structure for an automotive bumper, bumper fascia or bumper guard and more particularly to bumper fascia and bumper guards with thin stainless steel shells supported by and bonded directly to a substantially rigid, resiliently deformable plastic backing.
Further, the invention relates to a novel process for bonding ionomers such as Surlyn (Trade Mark of Dupont Company) to metals such as stainless steel and aluminum.
Automotive bumpers and bumper guards made entirely from metal are well known. These metal bumpers and bumper guards suffer the disadvantage of being excessively heavy, particularly where they are to have a sufficient thickness to reasonably resist permanent deformation on scratching or impact. Recently to reduce weight, many metal bumpers and bumper guards have been replaced by plastic or fiberglass bumpers and bumper guards. From a decorative point of view, however, bumpers and bumper guards are desired to have a chromed metallic appearance. To this end, many plastic bumpers and bumper guards have been provided with decorative inserts appearing as metal strips. Such strips may comprise an extremely thin metal foil covered by a transparent plastic protective layer. These known metal foil strips suffer the disadvantage that the appearance of the foil is easily marred by minor scratches and collisions. Presently known bumpers, bumper fascia and bumper guards suffer the disadvantages of failing to provide a practical product with a decorative yet functional metal outer surface at an acceptable cost and weight.
Accordingly, it is an object to at least partially overcome these disadvantages by providing a novel composite construction for bumpers, bumper fascia and bumper guards comprising a thin metallic skin-like layer supported by and bonded to a plastic backing.
In one of its aspects the present invention provides a construction for a component for an automotive bumper selected from the group consisting of an automotive bumper, a bumper fascia and a bumper guard, the construction comprising a laminate construction of a thin substantially rigid metal outer shell supported by a substantially rigid, resiliently deformable plastic backing bonded to the shell over substantially the entirety of an inner surface of the shell.
In the past attempts to secure plastic compounds to metals have not proven satisfactory, particularly, in respect of the process steps required for bonding, the cost and the nature of the plastic material and adhesive agents used and the strength of the bonds obtained. In particular, processes to secure zinc or sodium based ethylene ionomers such as Surlyn to stainless steel have suffered disadvantages in regard to providing satisfactorily strong bonds as are necessary in automotive bumper applications as well as in regard to providing practical implementation of such bonding processes at reasonable cost. For example processes involving the use of cylene primers for bonding of olefin polymers to metals have not proved satisfactory with ionomers. Such cylene primers require pre-heating to substantially high temperatures to provide activation energies necessary for useful bonding to Surlyn ionomers.
Accordingly it is a further object of the present invention to at least partially overcome these disadvantages by providing a novel process to bond ionomers such as zinc or sodium based ethylene ionomers preferably Surlyn to stainless steel through an intermediate layer of a co-polymer of polyethylene and an acrylic acid, preferably an ethylene acrylic acid co-polymer.
In another of its aspects the present invention provides a process to bond ionomers to metal comprising the steps of:
(1) bonding a thin intermediate layer of copolymer of polyethylene and an acrylic acid to the surface of the metal, and PA1 (2) injection moulding onto said intermediate layer said ionomers, PA1 wherein said co-polymers being sufficiently compatible with acid end groups of said ionomers to bond therewith. Preferably the process is carried out with zinc or sodium based ethylene ionomers and with co-polymers of polyethylene and an acrylic acid such as ethylene acrylic acid co-polymer and methacrylic acid co-polymer. The co-polymers preferably are selected to be similar to and compatible with acid end groups found in the ionomers to form strong bonds therewith.